Transition Metal Dichalcogenide MoS${}_2$: oxygen and fluorine functionalization for selective plasma processing

Abstract: Low-temperature plasma processing is a promising technique for tailoring the properties of transition metal dichalcogenides (TMDs) because it allows for precise control of radical and ion energies and fluxes. For chalcogen substitution, a key challenge is to identify the ion energy window that enables selective chalcogen removal while preserving the metal lattice. Using ab-initio molecular dynamics (AIMD), we demonstrate that oxygen and fluorine functionalization through thermal chemisorption significantly lowers the sputtering energy threshold ($E_{sputt}$) of MoS${}_2$ from $\sim 35$ eV to $\sim 10$ eV. In addition, we find that a non-orthogonal impact angle $\sim 30{}^{\circ}$ reduces the sputtering energy threshold, while cryogenic-range TMD temperatures may increase. To explain the observed trends, a multi-step sputtering mechanism is proposed. Our results show that oxygen/fluorine functionalization, impact angle, and material temperature are key control parameters for selective, damage-free chalcogen removal in TMD processing.